Apparatus to determine the mass of imbalance in a rotating tire is well known. See, for example, Great Britain Pat. No. 939,693 and Great Britain Pat. No. 1,247,596. See, additionally, U.S. Pat. Nos. 2,378,018; 2,828,911; 3,102,429; 3,724,279; 3,812,725; 3,835,712; 3,910,121; 3,911,751; 3,922,922; 3,991,620; and 4,173,146. See also U.S. Patent Application Ser. No. 238,091, filed on Feb. 25, 1981 in the name of Allan C. Madden and Albert L. Mitchell. All of the foregoing patents and patent application teach an apparatus to measure the force of imbalance of a rotating object, such as a tire. In general, all of the references teach an apparatus having a frame containing sensor means for determining the velocity of the tire, force transducer means for determining the magnitude of the force of imbalance, and calculating means for determining the position and magnitude of the imbalance in the tire.
The drive means for rotating the tire can be directly or indirectly coupled to the tire. Where the drive means is directly coupled to the tire, the drive means is directly mounted in the frame on a plate over the force transducers. A long shaft extends from the drive means to the tire.